1. Field of the Invention
This invention pertains generally to devices for monitoring chemical vapor, and more particularly to handheld/portable devices for monitoring chemical vapor.
2. Description of Related Art
Chemical vapor emission is a growing problem in occupational safety and industrial hygiene. Workers are exposed to numerous volatile hazardous chemicals daily. This problem can be much more serious when an emission source is nearby, e.g., in a chemical production line. In such a case, frequent evaluation and daily monitoring of the hazardous chemical vapor emission is absolutely necessary as the control of chemical exposure has and continues to present a major environmental and occupational problem. In this case, sensitive, field-portable monitoring techniques are needed to identify and control these chemical vapor emissions. The ability to monitor before, during, and after production processes is also necessary to provide experimental data for decisions regarding occupational safety and industrial hygiene.
Conventional portable and in-situ instruments for monitoring chemical vapors have certain limitations including limited selectivity, poor sensitivity, and limited quantitative capabilities. Laboratory-based instruments such as gas chromatography coupled with mass spectrometry (GC/MS) can provide the needed analytical power, but GC/MS is not amenable to timely response in the field. In most cases, several hours are needed to complete chemical vapor analyses using laboratory equipment. Existing portable GC/MS is powerful, but it can be complex to operate, difficult to maintain, expensive to build, and limited in portability and applicability. Chemical sensors based upon general physical or chemical properties typically rely upon non-specific detection, i.e., they are responsive only to changes in total vapor concentrations, and, therefore, they are not applicable to multi-component detection and can not be used in complex environmental conditions. In addition, such sensors can only provide incomplete information regarding the exact nature of the detected species, which makes it difficult to identify the chemical components in air emissions.
Ion mobility spectrometer (IMS) has long been considered as a potential tool for chemical vapor monitoring and chemical warfare detection since its advent in late 1960s. However, presently, the number of IMS instruments deployed as field monitors or detectors for real samples is still very limited because the instrument suffers problems of low resolution, poor selectivity, and severe memory effect. Other currently available portable instruments for chemical vapor monitoring are either low sensitivity or limited selectivity and can not meet the needs in chemical vapor monitoring.
Molecular emission spectrometry has long been used to quantify organic vapors. Various plasma sources have been used for molecular fragmentation and excitation, including microwave induced plasma, capacitively coupled plasma, inductively coupled plasma, and glow discharge. The advantage of these conventional plasmas is that they provide sufficient energy for molecular fragmentation and excitation. However, these plasmas usually need high power to run, from a few tens watts to thousands watts, and are unsuitable for portable detectors.
Accordingly, the present invention recognizes a clear requirement for a genuinely portable detector that can be applied for on-site chemical vapor and air emission monitoring.